The research proposed here is designed to advance our knowledge of disturbances affecting aphasic patients' abilities to understand sentences. Patients will be tested for their abilities to understand semantically irreversible sentences, semantically reversible sentences, and sentences in discourse context. Patients' performance as a function of these variables will serve to delineate three major types of impairments of the sentence comprehension process: (1) "lexico-pragmatic" comprehension: the ability to understand words and to integrate word meanings into sentence meanings on the basis of logical and pragmatic inferences based on real world knowledge; (2) "syntactic" comprehension: the ability to construct syntactic structures and use them to guide the integration of word meaning into sentence meaning; and (3) 'discourse' comprehension: the ability to use discourse structure to determine aspects of sentence meaning. Within each of these basic domains of sentence processing, we shall investigate the nature of patients' disturbances in a fine-grained manner, basing our detailed examination of these processes on models of sentence processing drawn from linguistics, psycholinguistics, computer science, and aphasiology. We will correlate specific disturbances of sentence comprehension with the location of brain lesions. The results will provide a detailed analysis of sentence comprehension disturbances in aphasia that makes direct contact with contempory models of sentence comprehension in cognitive science, and that can serve to test and extend these models. The results will also be of use in clinical patient diagnosis and in planning therapy.